Water-Based Ink for Ink-Jet Recording and Ink Container

ABSTRACT

There is provided a water-based ink for ink-jet recording including: water; a self-dispersible black pigment; and a resin-dispersed pigment of which hue angle is in a range of 180° to 270° and of which sedimentation velocity in the water-based ink is slower than sedimentation velocity of the self-dispersible black pigment in the water-based ink. A ratio (R/S) of a solid content weight (R) of the resin-dispersed pigment to a solid content weight (S) of the self-dispersible black pigment in the water-based ink is in a range of 0.26 to 0.80.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priority from Japanese Patent ApplicationNo. 2017-071134 filed on Mar. 31, 2017 the disclosure of which isincorporated herein by reference in its entirety.

BACKGROUND Field of the Invention

The present invention relates to a water-based ink for ink-jetrecording, and an ink container which accommodates the water-based inkfor ink-jet recording therein.

Description of the Related Art

In a water-based ink for ink-jet recording (hereinafter referred to alsoas a “water-based ink” or an “ink” in some cases), a pigment is widelyused as a colorant. In the water-based ink using the pigment, however,the particles of the pigment often sediment (settle) as time passes. Thesedimentation of the pigment particles causes a problem(s) such as theincrease in the viscosity of the water-based ink in the vicinity ofnozzles of an ink-jet head, any unsatisfactory jetting (discharge), anynon-uniform density in the water-based ink, etc.

As a solution to the above-described problem(s), there is proposed aself-dispersible dye-pigment containing a pigment, a polymer covalentlybonded to the pigment, a dye bonded to the polymer, and a dispersantcovalently bonded to at least one of the pigment, the polymer and thedye (see, for example, Japanese Patent Application Laid-open No.2006-176756 corresponding to U.S. Patent Application Publication Nos.US2006/0089421 and US2006/0089422).

In the above-described self-dispersible dye-pigment, however, it isnecessary to use the different kinds of the colorant that are thepigment and the dye; thus, any new method for addressing the pigmentsedimentation is required, in view of the stability, etc., of thewater-based ink. Further, regarding a water-based ink in which thepigment sedimentation is suppressed, there is a demand for a newwater-based ink for ink-jet recording in which the chromaticness C* issmaller and which is usable suitably as a water-based ink of anachromatic color such as black color, etc.

In view of the above-described situation, an object of the presentteaching is to provide a water-based ink for ink-jet recording which iscapable of suppressing the sedimentation of a self-dispersible blackpigment, in which the chromaticness C* is smaller, and which is suitablyusable as a water-based ink of the achromatic color such as black color,etc.

SUMMARY

According to a first aspect of the present teaching, there is provided awater-based ink for ink-jet recording including:

water;

a self-dispersible black pigment; and

a resin-dispersed pigment of which hue angle is in a range of 180° to270° and of which sedimentation velocity in the water-based ink isslower than sedimentation velocity of the self-dispersible black pigmentin the water-based ink,

wherein a ratio (R/S) of a solid content weight (R) of theresin-dispersed pigment to a solid content weight (S) of theself-dispersible black pigment in the water-based ink is in a range of0.26 to 0.80.

According to a second aspect of the present teaching, there is providedan ink container which accommodates the water-based ink for ink-jetrecording of the first aspect therein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph indicating, on a plane, “a*” and “b*” of each of0.002% by weight aqueous dispersion (water dispersion) of a carbon blackusable as a material of the self-dispersible black pigment, 0.003% byweight aqueous dispersion of C.I. Pigment Blue 60 (P.B. 60) and 0.002%by weight aqueous dispersion of C.I. Pigment Blue 15:3 (P.B. 15:3).

FIG. 2 is a schematic perspective view depicting the configuration of anexample of an ink-jet recording apparatus related to the presentteaching.

DESCRIPTION OF THE EMBODIMENTS

In the present teaching, the term “hue angle” represents, for example,an angle in the L*a*b* color system chromaticity diagram indicating a*and b* on the plane, and is defined as follows:

In a*≥0, b*≥0 (first quadrant), the hue angle=tan⁻¹(b*/a*);

In a*≤0, b*≥0 (second quadrant), the hue angle=180°+tan⁻¹(b*/a*);

In a*≤0, b*≤0 (third quadrant), the hue angle=180°+tan⁻¹(b*/a*); and

In a*≥0, b*≤0 (fourth quadrant), the hue angle=360°+tan⁻¹(b*/a*).

In the present teaching, the hue angle of the resin-dispersed pigment isdetermined, for example, by a method described in Examples (to bedescribed later on).

An explanation will be given about a water-based ink related to thepresent teaching. The water-based ink related to the present teachingcontains a colorant and water.

The colorant contains a self-dispersible black pigment, and aresin-dispersed pigment of which hue angle is in a range of 180° to270°.

The self-dispersible black pigment is dispersible in water without usingany dispersing agent, for example, owing to the fact that at least oneof the hydrophilic functional group and the salt thereof including, forexample, a carbonyl group, a hydroxyl group, a carboxylic acid group, asulfonic acid group, and a phosphate group is introduced into thesurfaces of the black pigment particles (such as particles of carbonblack) by the chemical bond directly or with any group interveningtherebetween. As the self-dispersible black pigment, it is possible touse a self-dispersible black pigment in which the carbon black issubjected to a treatment by any one of methods described, for example,in Japanese Patent Application Laid-open No. 8-3498 corresponding toU.S. Pat. No. 5,609,671, Published Japanese Translation of PCTInternational Publication for Patent Application No. 2000-513396corresponding to U.S. Pat. No. 5,837,045, Published Japanese Translationof PCT International Publication for Patent Application No. 2008-524400corresponding to U.S. Patent Application Publication No. US2006/0201380,Published Japanese Translation of PCT International Publication forPatent Application No. 2009-515007 corresponding to U.S. PatentApplication Publication No. US2007/0100023 and U.S. Patent ApplicationPublication No. US2007/0100024, Published Japanese Translation of PCTInternational Publication for Patent Application No. 2011-515535corresponding to U.S. Patent Application Publication No. US2009/0229489,etc. The carbon black, which is suitable to have the surface treatmentperformed therefor, includes, for example, carbon blacks such as “MA8”,“MA100” and “#2650” produced by MITSUBISHI CHEMICAL CORPORATION, etc. Asthe self-dispersible black pigment, it is allowable to use, for example,any commercially available product. The commercially available productincludes, for example, “CAB-O-JET (trade name) 200”, “CAB-O-JET (tradename) 300”, and “CAB-O-JET (trade name) 400” produced by CABOTCORPORATION; “BONJET (trade name) BLACK CW-2”, and “BONJET (trade name)BLACK CW-3” produced by ORIENT CHEMICAL INDUSTRIES, LTD.; and “LIOJET(trade name) WD BLACK 002C” produced by TOYO INK MFG. CO., LTD. It isallowable that only one kind of the self-dispersible black pigment asdescribed above is used singly, or two or more kinds of theself-dispersible black pigment are used in combination.

The hue angle of the self-dispersible black pigment is preferably withina range of 0° to 90°, more preferably within a range of 30° to 90°. Byallowing the hue angle of the self-dispersible black pigment to fallwithin this range, it is possible to obtain a water-based ink of whichchromaticness C* is smaller and which is suitably usable as anachromatic water-based ink having an achromatic color such as the blackcolor.

The resin-dispersed pigment (resin-dispersible pigment, resin dispersiontype pigment) is dispersible in water by, for example, apigment-dispersing resin (resin dispersant). As the resin dispersant, itis allowable to use a general resin dispersant. The resin-dispersedpigment may be encapsulated by the resin dispersant.

As described above, the hue angle of the resin-dispersed pigment iswithin the range of 180° to 270°. By allowing the hue angle of theresin-dispersed pigment to fall within the range of 180° to 270°, it ispossible to obtain a water-based ink of which chromaticness C* issmaller and which is suitably usable as an achromatic water-based inkhaving an achromatic color such as the black color.

It is preferred that the hue angle of the resin-dispersed pigment is ina range of 210° to 270°. The resin-dispersed pigment of which hue angleis in the range of 210° to 270° is exemplified, for example, by C.I.Pigment Blue 60 (P.B. 60) as an anthraquinone based pigment, C.I.Pigment Blue 15:3 (P.B. 15:3) as a copper phthalocyanine based pigment,etc. It is allowable that only one kind of the resin-dispersed pigmentas described above is used singly, or two or more kinds of theresin-dispersed pigment are used in combination.

As described above, it is allowable to use, as a the pigment-dispersingresin or the resin for dispersing pigment (resin dispersant), anypigment-dispersing resin of a general type, such as those exemplifiedby: proteins such as gelatin, albumin, casein, etc.; natural rubberssuch as gum arabic, gum traganth, etc.; glucosides such as saponin,etc.; naturally-occurring polymers such as lignin sulfonate, shellac,etc.; anionic polymers such as acrylic acid-acrylic acid ester copolymerand salt thereof, polyacrylate, polymethacrylate, salt ofstyrene-acrylic acid copolymer, salt of vinylnaphthalene-acrylic acidcopolymer, salt of styrene-maleic acid copolymer, salt of maleicacid-maleic anhydride copolymer, salt of vinylnaphthalene-maleic acidcopolymer, sodium salt of β-naphthalenesulfonic acid formalincondensate, orthophosphate, etc.; nonionic polymers such as polyvinylalcohol, polyvinyl pyrrolidone, etc.; and the like.

As described above, the resin-dispersed pigment may be encapsulated bythe resin dispersant. However, in view of suppressing the sedimentationof the self-dispersible black pigment, the resin-dispersed pigment ispreferably a pigment which is not encapsulated by the resin dispersant.A resin dispersant not encapsulating the pigment spreads in thewater-based ink more broadly (widely) as compared with a resindispersant encapsulating the pigment. This is presumed to realizefurther suppression of the sedimentation of the self-dispersible blackpigment.

The blending amount of the pigment-dispersing resin (resin dispersant)with respect to the entire amount of the water-based ink is notparticularly limited, and can be determined appropriately in accordancewith the kind of the resin-dispersed pigment, the pigment solid contentamount of the pigment, etc. The ratio of the solid content weight of theresin dispersant with respect to the pigment solid content weight of theresin-dispersed pigment in the water-based ink is, for example, in arange of 0.05 to 5.0 or in a range of 1.0 to 3.0.

TABLE 1 indicates L*, a*, b* and the hue angle of each of 0.002% byweight aqueous solution of a carbon black which is usable as a materialof the self-dispersible black pigment, 0.003% by weight aqueous solutionof P.B. 60 and 0.002% by weight aqueous solution of P.B. 15:3. Further,a graph indicating the a* and b* of each of these aqueous solutions on aplane is depicted in FIG. 1. Note that the mean particle diameter(average particle size) in TABLE 1 can be calculated, for example, byperforming dilution such that the solid content amount is in a range of0.02% by weight to 0.04% by weight and by performing measurement using adynamic light scattering particle diameter distribution measuringapparatus “LB-550” manufactured by HORIBA, LTD., with the intensity ofscattered light as the reference for the mean particle diameter. This isalso applicable to those described later on. Here, the “mean particlediameter (average particle size)” means an average particle size ofsecondary particles rather than primary particles. The “secondaryparticle” means a particle which is formed by an aggregation of theprimary particles. This is also applicable to those described later on.

TABLE 1 Carbon Black P.B. 60 P.B. 15:3 Mean particle 155 nm 120 nm 104nm diameter L* 42.59 61.70 74.70 a* 3.78 −2.80 −43.00 b* 15.75 −48.67−36.60 Hue angle (°) 76.50 266.71 220.40

In FIG. 1, pigments which are positioned relative to each other in pointsymmetrical positions, with the origin (a*=0, b*=0) as the center, havea relationship of complementary color. Each of P.B. 60 and P.B. 15:3 islocated in FIG. 1 at a closely symmetrical position about the originwith respect to the carbon black usable as a material of theself-dispersible black pigment. Accordingly, in a case that at least oneof P.B. 60 and P.B. 15:3 is used as the resin-dispersed pigment, it ispossible to obtain a water-based ink having a liquid color close to thatof a water-based ink containing only the self-dispersible black pigment,namely, to obtain a water-based ink of which chromaticness C* is smallerand which is suitably usable as an achromatic color ink having theachromatic color such as the black color. Among P.B. 60 and P.B. 15:3,it is preferred to use P.B. 60 located at a more closely symmetricalposition with respect to the carbon black, in view of the complementarycolor.

In view of obtaining an appropriate color (achromatic color) by makingthe chromaticness C* be small, as a value obtaining by subtracting thehue angle of the self-dispersible black pigment from the hue angle ofthe resin-dispersed pigment (the difference between the hue angle of theresin-dispersed pigment and the hue angle of the self-dispersible blackpigment) is closer to 180°, it is more preferred. The value (difference)is, for example, in a range of 140° to 220°, or in a range of 165° to195°.

In the water-based ink, the sedimentation velocity of theresin-dispersed pigment is slower than sedimentation velocity of theself-dispersible black pigment. Namely, the resin-dispersed pigment isharder (less likely) to sediment than the self-dispersible black pigmentin the water-based ink. With this, the sedimentation of theself-dispersible black pigment can be suppressed. Although the detailsof the mechanism of suppressing the sedimentation is not clear, it ispresumed that a resin dispersant for (dispersing) the resin-dispersedpigment suppresses the sedimentation of the self-dispersible blackpigment. This mechanism, however, is merely a presumption, and thepresent teaching is not limited to or restricted by this presumedmechanism.

The sedimentation velocity of the self-dispersible black pigment and thesedimentation velocity of the resin-dispersed pigment can be compared,for example, by an evaluation of sedimentation performed in Exampleswhich will be described later on. The evaluation of sedimentationincludes, for example: performing a predetermined centrifugingprocessing for each of a sample including the resin-dispersed pigmentand a sample including the self-dispersible black pigment; measuringviscosity before the centrifuging processing and viscosity after thecentrifuging processing in each of the sample including theresin-dispersed pigment and the sample including the self-dispersibleblack pigment; and calculating a viscosity increasing rate of theviscosity after the centrifuging processing with respect to theviscosity before the centrifuging processing in each of the sampleincluding the resin-dispersed pigment and the sample including theself-dispersible black pigment. In the evaluation of sedimentation, itis possible to determine that as the viscosity increasing rate of acertain sample is lower, the pigment in the certain sample is harder tosediment (is less likely to sediment). Namely, as a sample containingthe pigment therein has a smaller viscosity increasing rate, the pigmenthas a smaller (slower) sedimentation velocity. Accordingly, in thepresent teaching, the viscosity increasing rate of the sample includingthe resin-dispersed pigment is lower than the viscosity increasing rateof the sample including the self-dispersible black pigment.

The sedimentation velocities of the self-dispersible black pigment andthe resin-dispersed pigment can be adjusted each depending on thedensity, the mean particle diameter, etc., thereof. For example, bymaking the density of the self-dispersible black pigment to be higherthan the density of the resin-dispersed pigment, it is possible to makethe sedimentation velocity of the resin-dispersed pigment to be slowerthan the sedimentation velocity of the self-dispersible black pigment.Alternatively, for example, by making the mean particle diameter of theself-dispersible black pigment to be greater than the mean particlediameter of the resin-dispersed pigment, it is possible to make thesedimentation velocity of the resin-dispersed pigment to be slower thanthe sedimentation velocity of the self-dispersible black pigment.

For example, the density of the self-dispersible black pigment is in arange of 1.05 times to 1.88 times, in a range of 1.07 times to 1.78times, or in a range of 1.11 times to 1.58 times the density of theresin-dispersed pigment. Further, for example, the difference betweenthe density of the self-dispersible black pigment and the density of theresin-dispersed pigment is in a range of 0.18 g/cm³ to 0.77 g/cm³, or ina range of 0.25 g/cm³ to 0.55 g/cm³. The density of the self-dispersibleblack pigment is, for example, in a range of 1.8 g/cm³ to 2.1 g/cm³. Thedensity of the resin-dispersed pigment is, for example, in a range of1.3 g/cm³ to 1.6 g/cm³.

For example, the mean particle diameter (average particle size) of theself-dispersible black pigment is in a range of 1.05 times to 2.00times, in a range of 1.07 times to 1.75 times, or in a range of 1.08times to 1.49 times the mean particle diameter (average particle size)of the resin-dispersed pigment. Further, for example, the differencebetween the mean particle diameter of the self-dispersible black pigmentand the mean particle diameter of the resin-dispersed pigment is in arange of 5 nm to 100 nm, in a range of 7 nm to 70 nm, or in a range of 9nm to 51 nm. The mean particle diameter of the self-dispersible blackpigment is, for example, in a range of 135 nm to 210 nm, in a range of135 nm to 175 nm, or in a range of 135 nm to 155 nm. The mean particlediameter of the resin-dispersed pigment is, for example, is in a rangeof 80 nm to 150 nm, in a range of 100 nm to 126 nm, or in a range of 104nm to 120 nm.

A ratio (S:R) of a solid content weight (S) of the self-dispersibleblack pigment to a solid content weight (R) of the resin-dispersedpigment in the entire amount of the water-based ink is in a range ofS:R=1:0.26 to 1:0.80. Namely, the ratio (R/S) of the solid contentweight (R) of the resin-dispersed pigment to the solid content weight(S) of the self-dispersible black pigment in the water-based ink is in arange of 0.26 to 0.80. In view of the suppressing the sedimentation ofthe self-dispersible black pigment, the ratio (S:R) is preferably in arange of S:R=1:0.45 to 1:0.56 ((R/S)=0.45 to 0.56). The solid contentweight (R) is a weight only of the pigment, and does not include theweight of the resin dispersant. It is allowable that the solid contentweight (S) and the solid content weight (R) are appropriately adjustedsuch that the ratio S:R=1:0.26 to 1:0.80 is provided; the solid contentweight (S) is, for example, in a range of 1.0% by weight to 7.0% byweight, in a range of 3.0% by weight to 5.0% by weight, or in a range of3.5% by weight to 4.5% by weight; and the solid content weight (R) is,for example, in a range of 0.26% by weight to 5.6% by weight, in a rangeof 0.78% by weight to 4.0% by weight, or in a range of 0.91% by weightto 3.6% by weight.

A sum (S+R) of the solid content weight (S) and the solid content weight(R) is, for example, in a range of 4% by weight to 11% by weight, in arange of 5% by weight to 8% by weight, or in a range of 5% by weight to6% by weight.

It is allowable that the water-based ink also additionally contains acolorant, such as a pigment, a dye, etc., different from theself-dispersible black pigment and the resin-dispersed pigment of whichhue angle is within the range of 180° to 270°; or it is allowable thatthe water-based ink does not contain any colorant, such as a pigment, adye, etc., different from the self-dispersible black pigment and theresin-dispersed pigment of which hue angle is within the range of 180°to 270°. However, in view of obtaining an appropriate color (achromaticcolor) by making the chromaticness C* be small, it is preferred that thecolorant is substantially composed of the self-dispersible black pigmentand the resin-dispersed pigment of which hue angle is within the rangeof 180° to 270°. Further, from a similar viewpoint as described above,it is preferred that the colorant is substantially composed of theself-dispersible black pigment of which hue angle is within the range of0° to 90° and the resin-dispersed pigment of which hue angle is withinthe range of 180° to 270°. A rate of the sum (S+R) of the solid contentweight (S) of the self-dispersible black pigment and the solid contentweight (R) of the resin-dispersed pigment with respect to the entireweight of the colorant is, for example, in a range of 95% by weight to100% by weight, or in a range of 98% by weight to 100% by weight.

The water is preferably ion-exchange water or purified water (purewater). The blending amount of the water with respect to the entireamount of the water-based ink may be, for example, a balance of theother components.

The water-based ink may further contain a water-soluble organic solvent.The water-soluble organic solvent is exemplified, for example, by ahumectant which prevents the water-based ink from drying at an end of anozzle in an ink-jet head, a penetrant which adjusts the drying velocityon a recording medium, etc.

The humectant is not particularly limited, and is exemplified, forexample, by lower alcohols such as methyl alcohol, ethyl alcohol,n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol,and tert-butyl alcohol; amides such as dimethylformamide anddimethylacetamide; ketones such as acetone; ketoalcohols (ketonealcohols) such as diacetone alcohol; ethers such as tetrahydrofuran anddioxane; polyethers such as polyalkylene glycol; polyvalent alcoholssuch as alkylene glycol, glycerol, trimethylolpropane,trimethylolethane, etc.; 2-pyrrolidone; N-methyl-2-pyrrolidone;1,3-dimethyl-2-imidazolidinone; and the like. The polyalkylene glycol isexemplified, for example, by polyethylene glycol, polypropylene glycol,etc. The alkylene glycol is exemplified, for example, by ethyleneglycol, propylene glycol, butylene glycol, diethylene glycol,triethylene glycol, dipropylene glycol, tripropylene glycol,thiodiglycol, hexylene glycol, etc. It is allowable that only one kindof the humectant as described above is used singly, or two or more kindsof the humectant are used in combination. Among the above-describedhumectants, the humectant is preferably a polyvalent alcohol such asalkylene glycol, glycerol, etc.

The blending amount of the humectant in the entire amount of thewater-based ink is, for example, in a range of 0% by weight to 95% byweight, in a range of 5% by weight to 80% by weight, or in a range of 5%by weight to 50% by weight.

The penetrant is not particularly limited, and is exemplified, forexample, by glycol ether. The glycol ether is not particularly limited,and is exemplified, for example, by ethylene glycol methyl ether,ethylene glycol ethyl ether, ethylene glycol-n-propyl ether, diethyleneglycol methyl ether, diethylene glycol ethyl ether, diethyleneglycol-n-propyl ether, diethylene glycol-n-butyl ether, diethyleneglycol-n-hexyl ether, triethylene glycol methyl ether, triethyleneglycol ethyl ether, triethylene glycol-n-propyl ether, triethyleneglycol-n-butyl ether, propylene glycol methyl ether, propylene glycolethyl ether, propylene glycol-n-propyl ether, propylene glycol-n-butylether, dipropylene glycol methyl ether, dipropylene glycol ethyl ether,dipropylene glycol-n-propyl ether, dipropylene glycol-n-butyl ether,tripropylene glycol methyl ether, tripropylene glycol ethyl ether,tripropylene glycol-n-propyl ether, tripropylene glycol-n-butyl ether,etc. One type of the penetrant may be used singly, or two or more kindsof the penetrant may be used in combination.

The blending amount of the penetrant in the entire amount of thewater-based ink is, for example, in a range of 0% by weight to 20% byweight, in a range of 0% by weight to 15% by weight, or in a range of 1%by weight to 6% by weight.

The water-based ink may further contain an anionic surfactant. Theanionic surfactant is exemplified, for example, by alkyl sulfuric acidsalt, alkyl ester sulfuric acid salt, alkyl ether sulfuric acid estersalt, alkylbenzene sulfonate, alkyl phosphate, α-olefin sulfonate sodiumsalt (sodium α-olefin sulfonate), sulfosuccinic acid, etc. As theanionic surfactant, for example, a commercially available product may beused. The commercially available product is exemplified, for example, byanionic surfactants produced by LION SPECIALTY CHEMICALS CO., LTD.,including “LIPOLAN (trade name)” series, “LIPON (trade name)” series,“SUNNOL (trade name)” series, “LIPOTAC (trade name) series, ENAGICOL(trade name)” series, “LIPAL (trade name)” series, and “LOTAT (tradename)” series, etc.; anionic surfactants produced by KAO CORPORATIONincluding “EMAL (trade name)” series, “LATEMUL (trade name)” series,“VENOL (trade name)” series, “NEOPELEX (trade name)” series, NS SOAP, KSSOAP, OS SOAP, and “PELEX (trade name)” series, etc.; anionicsurfactants produced by SANYO CHEMICAL INDUSTRIES, LTD. including“SANDET (trade name)” series and “BEAULIGHT (trade name)” series, etc.;anionic surfactants produced by TOHO CHEMICAL INDUSTRY CO., LTD.including “ALSCOPE (trade name)” series, “NEOSCOPE (trade name)” series,“PHOSFANOL (trade name)” series, etc.; sodium hexadecyl sulfate, sodiumstearyl sulfate, etc. produced by TOKYO CHEMICAL INDUSTRY CO., LTD.; andthe like.

The blending amount of the anionic surfactant in the entire amount ofthe water-based ink is, for example, not more than 5% by weight, notmore than 3% by weight, or in a range of 0.1% by weight to 2% by weight.

The water-based ink may further contain a nonionic surfactant. As thenonionic surfactant, it is allowable to use, for example, a commerciallyavailable product. The commercial available product is exemplified, forexample, by “OLFIN (trade name) E1010”, “OLFIN (trade name) E1004”,etc., produced by NISSHIN KAGAKU KOGYO KK, etc.

The blending amount of the nonionic surfactant in the entire amount ofthe water-based ink is, for example, not more than 5% by weight, notmore than 3% by weight, or in a range of 0.1% by weight to 2% by weight.

The water-based ink may further contain a resin, in addition to theresin dispersant, for the purpose of improving the fixing property ofthe water-based ink.

The water-based ink may further contain a conventionally known additive,as necessary. The additive is exemplified, for example, by pH-adjustingagents, viscosity-adjusting agents, surface tension-adjusting agents,fungicides, etc. The viscosity-adjusting agents are exemplified, forexample, by polyvinyl alcohol, cellulose, etc.

The water-based ink can be prepared, for example, by uniformly mixingthe self-dispersible black pigment, the resin-dispersed pigment, water,and an optionally another additive(s) as necessary, by a known method,and then removing any non-dissolved matter, etc., with a filter, etc.

As described above, according to the present teaching, by using theself-dispersible black pigment and the resin-dispersed pigment of whichhue angle is within a predetermined range, in combination under apredetermined condition, it is possible to provide a water-based ink forink-jet recording which is capable of suppressing the sedimentation ofthe self-dispersible black pigment, of which chromaticness C* issmaller, and which is usable suitably as a water-based ink of theachromatic color such as the black color, etc.

Next, an ink cartridge (an example of an ink container) of the presentteaching will be explained. The ink cartridge of the present teaching ischaracterized by being an ink cartridge containing a water-based ink forink-jet recording; wherein the water-based ink is the water-based inkfor ink-jet recording of the present teaching as described above.Namely, the ink cartridge (ink container) related to the presentteaching contains the water-based ink for ink-jet recording of thepresent teaching in the inside thereof. Any known main body (body) of anink cartridge can be used as the main body of the ink cartridge of thepresent teaching.

Next, explanation will be given about an ink-jet recording apparatusrelated to the present teaching.

The ink-jet recording apparatus related to the present teaching is anink-jet recording apparatus characterized by including: an inkaccommodating section configured to accommodate an ink therein; and anink discharge mechanism configured to discharge the ink accommodated inthe ink accommodating section; wherein the ink accommodated in the inkaccommodating section is the water-based ink for ink-jet recordingrelated to the present teaching.

FIG. 2 depicts the configuration of an example of the ink-jet recordingapparatus related to the present teaching. As depicted in FIG. 2, anink-jet recording apparatus 1 related to the present teaching includesfour ink cartridges (ink containers) 2, an ink discharge mechanism(ink-jet head) 3, a head unit 4, a carriage 5, a driving unit 6, aplaten roller 7 and a purge device 8 as main constitutive components orparts.

The four ink cartridges 2 contain water-based inks of four colors,respectively, the four colors being yellow, magenta, cyan and black. Forexample, the water-based black ink is the water-based ink for ink-jetrecording related to the present teaching. In this example, a set of thefour ink cartridges 2 is described. However, it is allowable to use anintegrated ink cartridge of which interior (inner part) is partitionedso as to form an accommodating section for the water-based yellow ink,an accommodating section for the water-based magenta ink, anaccommodating section for the water-based cyan ink and an accommodatingsection for the water-based black ink, instead of using the set of thefour ink cartridges 2. As the body of the ink cartridge, it is possibleto use, for example, a publicly known body.

The ink-jet head 3 disposed on the head unit 4 performs recording on arecording medium (for example, recording paper or recording sheet) P.The four ink cartridges 2 and the head unit 4 are provided or arrangedon the carriage 5. The driving unit 6 reciprocates the carriage 5 in alinear direction. As the driving unit 6, it is possible to use, forexample, a known driving unit (see, for example, Japanese PatentApplication laid-open No. 2008-246821 corresponding to United StatesPatent Application Publication No. US2008/0241398). The platen roller 7extends in the reciprocating direction of the carriage 5 and is arrangedto face or be opposite to the ink-jet head 3.

The purge device 8 sucks or draws unsatisfactory ink (poor ink) whichcontains air bubbles, etc. accumulated or trapped in the inside of theink-jet head 3. As the purge device 8, it is possible to use, forexample, a known purge device (see, for example, Japanese PatentApplication laid-open No. 2008-246821 corresponding to United StatesPatent Application Publication No. US2008/0241398).

A wiper member 20 is provided on the purge device 8, at a position onthe side of the platen roller 7 such that the wiper member 20 isadjacent to the purge device 8. The wiper member 20 is formed to have aspatula shape, and wipes a nozzle-formed surface of the ink-jet head 3accompanying with the movement (reciprocating movement) of the carriage5. In FIG. 2, a cap 18 is provided to cover a plurality of nozzles ofthe ink-jet head 3 which is returned to a reset position upon completionof the recording, so as to prevent the water-based inks from drying.

In the ink-jet recording apparatus 1 of the present embodiment, the fourink cartridges 2 are provided, together with the head unit 4, on onecarriage 5. However, the present teaching is not limited to this. In theink-jet recording apparatus 1, the respective four ink cartridges 2 maybe provided on a carriage which is different (separate) from thecarriage on which the head unit 4 is provided. Alternatively, therespective four ink cartridges 2 may be arranged and fixed inside theink-jet recording apparatus 1, rather than being provided on thecarriage 5. In such aspects, for example, each of the four inkcartridges 2 and the head unit 4 which is provided on the carriage 5 areconnected with a tube, etc., and the water-based inks are supplied fromthe four cartridges 2, respectively, to the head unit 4 via the tubes.Further, in these aspects, it is allowable to use, as the inkcontainers, four ink bottles having a bottle shape, instead of using thefour ink cartridges 2. In such a case, each of the ink bottles may beprovided with an inlet port via which the ink is poured from the outsideto the inside of the ink bottle.

Ink-jet recording using the ink-jet recording apparatus 1 is performed,for example, in the following manner. Namely, at first, a recordingpaper P is supplied or fed, for example, from a paper feeding cassetteor sheet feeding cassette (not depicted in the drawing) arranged at aside of or at a position below the ink-jet recording apparatus 1. Therecording paper P is introduced or guided between the ink-jet head 3 andthe platen roller 7. Then, a predetermined recording is performed on thefed or introduced recording paper P with the water-based ink(s)discharged or jetted from the ink-jet head 3. According to the presentteaching, the sedimentation of the pigment is suppressed, and thus anydischarge failure (jetting failure) in the ink-jet head 3 is suppressed.The recording paper P after the recording is discharged from the ink-jetrecording apparatus 1. According to the present teaching, it is possibleto obtain a recorded matter in which the black color is close to anachromatic color obtained in a case of using a water-based inkcontaining only the self-dispersible black pigment, and in which thenon-uniform density is suppressed. In FIG. 2, the paper feedingmechanism and paper discharge mechanism for the recording paper P areomitted in the drawing.

In the apparatus depicted in FIG. 2, an ink-jet head of serial type(serial type ink-jet head) is adopted. However, the present teaching isnot limited to this. The ink-jet recording apparatus may be an apparatusadopting an ink-jet head of line type (line type ink-jet head).

Next, an ink-jet recording method related to the present teaching is anink-jet recording method characterized by including: performingrecording on a recording medium by discharging, to the recording medium,a water-based ink by an ink-jet system; and using the water-based inkfor ink-jet recording related to the present teaching, as thewater-based ink. The recording includes printing a letter (text),printing an image, printing, etc.

EXAMPLES

Next, examples related to the present teaching will be explainedtogether with comparative examples. Note that the present teaching isnot limited to and is not restricted by the examples and the comparativeexamples which will be described below.

<Preparation of Aqueous Pigment Dispersion 1>

40 g of Carbon Black “#2650” produced by MITSUBISHI CHEMICAL CORPORATIONwas mixed with 200 g of ion-exchanged water, followed by beingpulverized by a bead mill. The pulverized mixture was added with acarboxyl group agent, followed by being heated and agitated, andsubjected to an oxidation processing. The obtained liquid was cleanedwith a solvent for several times, was poured into water, and was cleanedagain with the water in a repeated manner. Then, the liquid wasfiltrated with a filter, and thus a water (aqueous) pigment dispersion 1indicated in TABLE 2 was obtained. The mean particle diameter (averageparticle size) of the carbon black contained in the aqueous pigmentdispersion 1 was measured by using the dynamic light scattering particlediameter distribution measuring apparatus “LB-550” (product name)manufactured by HORIBA, LTD., and the mean particle diameter was 155 nm.

<Preparation of Aqueous Pigment Dispersions 2 to 4>

Aqueous pigment dispersions 2, 3 and 4 in each of which a pigment wasdispersed in water by a dispersant were prepared by the followingmethod. Pure water (purified water) was added to 20% by weight of apigment (P.B. 60) and 7% by weight of a styrene-acrylic acid copolymerneutralized by sodium hydroxide (acid value: 175 mgKOH/g, molecularweight: 10000) so that the entire amount thereof was 100% by weight,followed by being agitated and mixed, and thus a mixture was obtained.The obtained mixture was placed in a wet sand mill charged with zirconiabeads of which diameter was 0.3 mm, and was subjected to a dispersingprocess for 6 hours. Afterwards, the zirconia beads were removed by aseparator, and the mixture was filtrated through a cellulose acetatefilter (pore size 3.0 μm). Thus, aqueous pigment dispersion 2 indicatedin TABLE 2 was obtained. Note that the styrene-acrylic acid copolymer isa water-soluble polymer which is generally used as a dispersant forpigment (pigment dispersant). Further, aqueous pigment dispersions 3 and4 indicated in TABLE 2 were obtained in a similar manner regarding theaqueous pigment dispersion 2 except for appropriately changing the kindof pigment, the component rate and the duration time of dispersingprocess. Note that in the legend of TABLE 2, “P.R. 122” represents C.I.pigment red 122.

Examples 1 to 12 and Comparative Examples 1 to 8

Components, except for the aqueous pigment dispersions 1 to 4, whichwere included in Water-based Ink Composition (TABLE 2) were mixeduniformly or homogeneously; and thus an ink solvent was obtained.Subsequently, the ink solvent was added to the aqueous pigmentdispersion 1 and to any one of the aqueous pigment dispersion 2 to 4 (inComparative Example 1, only to the aqueous pigment dispersion 1),followed by being mixed uniformly, and thus a mixture was obtained.After that, the obtained mixture was filtrated through a celluloseacetate membrane filter (pore size 3.00 μm) produced by TOYO ROSHIKAISHA, LTD., and thus a water-based ink for ink jet recording of eachof Examples 1 to 12 and Comparative Examples 1 to 8 indicated in TABLE 2was obtained. Note that in the legend of TABLE 2, the hue angles of theaqueous solutions of the self-dispersible black pigment, P.B. 60, P.B.15:3 and P.R. 122 were obtained with the following method.

<Method for Obtaining Hue Angle>

Regarding a 0.002% by weight aqueous solution of the self-dispersibleblack pigment, a 0.003% by weight aqueous solution of P.B. 60, a 0.002%by weight aqueous solution of P.B. 15:3 and a 0.004% by weight aqueoussolution of P.R. 122, color measurement was performed using aspectrophotometer UV 3600 manufactured by SHIMADZU CORPORATION, for ameasuring cell having a cell length of 10 mm with pure water (purifiedwater) as the reference, and thus the L* value, the a* value and b*value were obtained for each of the above-described aqueous solutions.Each of the L* value, the a* value and b* value is based on the L*a*bcolor system (CIE 1976 (L*a*b*) color system) normalized in 1976 byCommission Internationale d'Eclairage (CIE) (see JIS Z 8729). From thea* value and b* value, the hue angle was obtained by the above-describeddefinition equation of the hue angle.

With respect to the water-based inks of Examples 1 to 12 and ComparativeExamples 1 to 8, respectively, (a) Evaluation of sedimentation and (b)Evaluation of the color (tone, tint) of liquid were performed by thefollowing methods.

(a) Evaluation of Sedimentation

40 mL of the water-based ink of each of the examples and the comparativeexamples was placed in a 50 mL centrifugal settling tube, and wassubjected to a centrifuging processing using a High-speed microcentrifugal CF16RXII and Angle Rotor: T6AP31 manufactured by HITACHIKOKI CO., LTD., under a condition of 6,000 rpm and for 10 minutes.Afterwards, 2 mL of the water-based ink was taken out from a bottom partof the centrifugal settling tube, the viscosity of the water-based inkwas measured, and the viscosity increasing rate from the initialviscosity before the centrifuging processing was calculated. Theviscosity is a value measured at 25° C. by using a viscometer TVE-25manufactured by TOM SANGYO CO., LTD. Note that the viscosity increasingrate in water-based inks (samples) in each of which one of the aqueouspigment dispersions 1 to 4 was diluted with water such that the pigmentsolid content weight became to be 4% by weight (such that the initialviscosity became about 4 mPa·s) was as follows. As the viscosityincreasing rate of a water-based ink is lower, it is possible todetermine that the sedimentation of the pigment is harder to occur (lesslikely to occur or hardly occurs) in the water-based ink. Namely, in theevaluation of the sedimentation, it is possible to determine that as asample (water-based ink) containing the pigment therein has a smallerviscosity increasing rate, the pigment has a smaller sedimentationvelocity.

Viscosity increasing rate Aqueous pigment dispersion 1 (self-dispersible30% black pigment) Aqueous pigment dispersion 2 (P.B. 60) 12% Aqueouspigment dispersion 3 (P.B. 15:3) 10% Aqueous pigment dispersion 4 (P.R.122) 12%

<Criterion for Evaluation of Sedimentation>

AA: The viscosity increasing rate was less than 26%.

A: The viscosity increasing rate was in a range of not less than 26% toless than 29%.

B: The viscosity increasing rate was not less than 29%.

(b) Evaluation of Color of Liquid

The water-based ink of each of the examples and the comparative exampleswas diluted such that the solid content weight of the pigment became0.002% by weight, the color measurement was performed using thespectrophotometer UV 3600, for a measuring cell having a cell length of10 mm with pure water (purified water) as the reference, and thus the L*value, the a* value and b* value were obtained for the water-based inkof each of the examples and the comparative examples. Each of the L*value, the a* value and b* value is based on the L*a*b color system (CIE1976 (L*a*b*) color system) normalized in 1976 by CommissionInternationale d'Eclairage (CIE) (see JIS Z 8729). From the a* value andb* value, the chromaticness C* was calculated by the followingexpression, and the evaluation was made based on the following criterionof the evaluation. Note that as appreciated from the followingexpression, the chromaticness C* corresponds to a distance, in the graphindicating a* and b* on a plane, from the position of the water-basedink of each of the examples and the comparative examples to origin: a*=0and b*=0; as the chromaticness C* of a water-based ink is smaller, it ispossible to determine that the water-based ink is more preferred as anachromatic color water-based ink such as a black water-based ink, etc.

C*={(a ^(*2))+(b ^(*2))}^(1/2)

<Criterion for Evaluation of Color of Liquid>

AA: C* is less than 10.

A: C* is in a range of not less than 10 to less than 20.

B: C* is not less than 20.

The water-based ink composition and the results of evaluations of eachof the water-based inks of Examples 1 to 12 and Comparative Examples 1to 8 are indicated in TABLE 2.

Table 2 (Following)—Legend

-   -   1: Aqueous dispersion of self-dispersible black pigment; hue        angle: 76.50°; mean particle diameter: 155 nm; numeral in the        table indicates pigment solid content weight; density of        pigment: 1.8 g/cm³.    -   2: Aqueous dispersion of P.B. 60 (containing resin dispersant);        hue angle: 266.71°; mean particle diameter: 120 nm; numeral in        the table indicates pigment solid content weight; density of        pigment: 1.3 g/cm³.    -   3: Aqueous dispersion of P.B. 15:3 (containing resin        dispersant); hue angle: 220.40°; mean particle diameter: 104 nm;        numeral in the table indicates pigment solid content weight;        density of pigment: 1.62 g/cm³.    -   4: Aqueous dispersion of P.R. 122 (containing resin dispersant);        hue angle: 330.36°; mean particle diameter: 126 nm; numeral in        the table indicates pigment solid content weight; density of        pigment: 1.5 g/cm³.    -   5: Surfactant, manufactured by LION SPECIALTY CHEMICALS CO.,        LTD.; effective ingredient amount: 28% by weight; numeral in the        table indicates the effective ingredient amount.

The unit in the water-based ink composition in TABLE 2: % by weight

TABLE 2 EXAMPLES 1 2 3 4 5 6 Water-based ink Aqueous pigment dispersion1 (S) (*1) 3.75 3.75 3.75 3.75 3.75 7.00 Composition Aqueous pigmentdispersion 2 (R) (*2) 1.00 1.70 2.00 2.10 3.00 3.50 (% by weight)Aqueous pigment dispersion 3 (R) (*3) — — — — — — Aqueous pigmentdispersion 4 (R) (*4) — — — — — — Glycerol 27.50  25.20  24.50  23.40 20.30  16.00  Triethylene glycol-n-butyl ether 5.00 5.00 5.00 5.00 5.005.00 SUNNOL (trade name) NL1430 (*5) 1.00 1.00 1.00 1.00 1.00 1.00 Waterbalance balance balance balance balance balance S:R 1:0.27 1:0.45 1:0.531:0.56 1:0.80 1:0.50 Evaluation of sedimentation A AA AA AA A AAEvaluation of color of liquid AA AA AA AA AA AA EXAMPLES 7 8 9 10 11 12Water-based ink Aqueous pigment dispersion 1 (S) (*1) 3.80 3.80 3.803.80 3.80 7.00 Composition Aqueous pigment dispersion 2 (R) (*2) — — — —— — (% by weight) Aqueous pigment dispersion 3 (R) (*3) 1.00 1.70 2.032.10 3.00 3.50 Aqueous pigment dispersion 4 (R) (*4) — — — — — —Glycerol 28.00  27.10  26.50  25.50  22.70  17.50  Triethyleneglycol-n-butyl ether 5.00 5.00 5.00 5.00 5.00 5.00 SUNNOL (trade name)NL1430 (*5) 1.00 1.00 1.00 1.00 1.00 1.00 Water balance balance balancebalance balance balance S:R 1:026 1:0.45 1:0.53 1:0.55 1:0.79 1:0.50Evaluation of sedimentation A AA AA AA A AA Evaluation of color ofliquid AA A A A A AA COMPARATIVE EXAMPLES 1 2 3 4 5 6 7 8 Water-basedink Aqueous pigment dispersion 1 (S) (*1) 3.75 3.75 3.75 3.75 3.80 3.803.80 3.75 Composition Aqueous pigment dispersion 2 (R) (*2) — 0.90 3.103.75 — — — — (% by weight) Aqueous pigment dispersion 3 (R) (*3) — — — —0.95 3.10 3.80 — Aqueous pigment dispersion 4 (R) (*4) — — — — — — —2.04 Glycerol 29.10  18.50  18.50  18.50  20.30  20.30  20.30  26.30 Triethylene glycol-n-butyl ether 5.00 5.00 5.00 5.00 5.00 5.00 5.00 5.00SUNNOL (trade name) NL1430 (*5) 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00Water balance balance balance balance balance balance balance balanceS:R — 1:0.24 1:0.83 1:1 1:0.25 1:0.82 1:1 1:0.54 Evaluation ofsedimentation B B B B B B B AA Evaluation of color of liquid A AA AA AAAA A B B

As indicated in TABLE 2, in Examples 1 to 12, the result of evaluationof sedimentation and the result of evaluation of color of liquid weresatisfactory. In Examples 2 to 4, 6, 8 to 10 and 12 each satisfyingS:R=1:0.45 to 1:0.56 (R/S=0.45 to 0.56), the result of evaluation ofsedimentation was particularly excellent. Further, in Examples 1 to 6each using P.B. 60 as the self-dispersible black pigment, the result ofevaluation of color of liquid was particularly excellent.

On the other hand, in Comparative Example 1 which did not use theresin-dispersed pigment and Comparative Examples 2 to 7 in each of whichR/S was less than 0.26 or exceeded 0.80, either one or both of theresult of evaluation of sedimentation and the result of evaluation ofcolor of liquid was/were unsatisfactory. Further, in Comparative Example8 using, as the resin-dispersed pigment, P.R. 122 of which hue angle wasnot in the range of 180° to 270°, the result of evaluation of color ofliquid was unsatisfactory.

As described above, the water-based ink related to the present teachingis capable of suppressing the sedimentation of the self-dispersibleblack pigment, has the chromaticness C* which is smaller, and issuitably usable as a water-based ink of the achromatic color such asblack color, etc. The applicability of the water-based ink related tothe present teaching is not particularly limited, and is widelyapplicable to a variety of kinds of ink-jet recording.

What is claimed is:
 1. A water-based ink for ink-jet recording comprising: water; a self-dispersible black pigment; and a resin-dispersed pigment of which hue angle is in a range of 180° to 270° and of which sedimentation velocity in the water-based ink is slower than sedimentation velocity of the self-dispersible black pigment in the water-based ink, wherein a ratio (R/S) of a solid content weight (R) of the resin-dispersed pigment to a solid content weight (S) of the self-dispersible black pigment in the water-based ink is in a range of 0.26 to 0.80.
 2. The water-based ink for ink-jet recording according to claim 1, wherein the ratio (R/S) of the solid content weight (R) of the resin-dispersed pigment to the solid content weight (S) of the self-dispersible black pigment in the water-based ink is in a range of 0.45 to 0.56.
 3. The water-based ink for ink-jet recording according to claim 1, wherein the hue angle of the resin-dispersed pigment is in a range of 210° to 270°
 4. The water-based ink for ink-jet recording according to claim 1, wherein the resin-dispersed pigment is at least one of an anthraquinone based pigment and a copper phthalocyanine based pigment.
 5. The water-based ink for ink-jet recording according to claim 4, wherein the resin-dispersed pigment is at least one of C.I. Pigment Blue 60 and C.I. Pigment Blue 15:3.
 6. The water-based ink for ink-jet recording according to claim 5, wherein the resin-dispersed pigment is the C.I. Pigment Blue
 60. 7. The water-based ink for ink-jet recording according to claim 1, wherein the self-dispersible black pigment is carbon black.
 8. The water-based ink for ink-jet recording according to claim 1, wherein a hue angle of the self-dispersible black pigment is in a range of 0° to 90°.
 9. The water-based ink for ink-jet recording according to claim 1, wherein mean particle diameter of the self-dispersible black pigment is in a range of 1.05 times to 2.00 times mean particle diameter of the resin-dispersed pigment.
 10. The water-based ink for ink-jet recording according to claim 9, wherein difference between the mean particle diameter of the self-dispersible black pigment and the mean particle diameter of the resin-dispersed pigment is in a range of 5 nm to 100 nm.
 11. The water-based ink for ink-jet recording according to claim 1, wherein density of the self-dispersible black pigment is in a range of 1.05 times to 1.88 times density of the resin-dispersed pigment.
 12. The water-based ink for ink-jet recording according to claim 11, wherein difference between the density of the self-dispersible black pigment and the density of the resin-dispersed pigment is in a range of 0.18 g/cm³ to 0.77 g/cm³.
 13. The water-based ink for ink-jet recording according to claim 1, wherein a sum (S+R) of the solid content weight (S) of the self-dispersible black pigment and the solid content weight (R) of the resin-dispersed pigment in the water-based ink is in a range of 4% by weight to 11% by weight.
 14. The water-based ink for ink-jet recording according to claim 1, wherein the resin-dispersed pigment is harder to sediment than the self-dispersible black pigment in the water-based ink.
 15. The water-based ink for ink-jet recording according to claim 1, wherein in an evaluation of sedimentation, a viscosity increasing rate of a sample including the resin-dispersed pigment is lower than a viscosity increasing rate of a sample including the self-dispersible black pigment, the evaluation of the sedimentation including: performing a predetermined centrifuging processing for each of the sample including the resin-dispersed pigment and the sample including the self-dispersible black pigment; measuring viscosity before the centrifuging processing and viscosity after the centrifuging processing in each of the sample including the resin-dispersed pigment and the sample including the self-dispersible black pigment; and calculating a viscosity increasing rate of the viscosity after the centrifuging processing to the viscosity before the centrifuging processing in each of the sample including the resin-dispersed pigment and the sample including the self-dispersible black pigment.
 16. An ink container which accommodates the water-based ink for ink-jet recording as defined in claim
 1. 